The present invention relates to a data collection system for reading the indications of watt-hour meters, watermeters or gas meters distributed over remote locations.
There have been proposed various systems for collecting the indications of watt-hour meters, gas meters or water meters installed in respective homes and buildings. However the remote terminal equipment of the prior art data collection systems is in general provided with a power source and a clock pulse generator so that the indication of a meter may be read in response to the clock pulses. As a result the remote terminal equipment is rather expensive. Furthermore when the power source consists of batteries, misreading results due to the voltage drop and the batteries must be replaced periodically. Thus from the standpoint of system accuracy and maintenance, the prior art data collection systems are not satisfactory in practice. In order to overcome these problems there has been proposed a data collection system where the power is supplied from the centralized data terminal to each remote terminal equipment. However this system needs additional power transmission lines in addition to the data transmission lines so that the installation costs will increase and the system itself becomes complex. There has been proposed another data collection system wherein the clock pulses are transmitted from the centralized data terminal to each remote terminal equipment so as to eliminate the provision of a clock generator in each remote terminal equipment. However the amplitude of the clock pulses varies due to the influences of electrical resistance of the transmission line interconnecting between the centralized data terminal and each remote terminal equipment so that misreadings tend to occur often. There has been further proposed a data collection system wherein the centralized data terminal transmits the clock pulses to each remote terminal equipment so that not only the reading may be obtained in response to the clock pulses but also some clock pulses may be used to provide a power source. However since the clock pulses are used not only as the power signal but also as the data signal, they tend to become unstable, resulting in the misreading.